Biomedical subjects

M Lassonde

Publications and source records attributed to M Lassonde.

At least 55 records · Page 3Linked to original sources

PubMed1993

Dreaming in agenesis of the corpus callosum: laboratory and home assessment of four cases.

Laboratory and home dream recall was studied in four subjects with agenesis of the corpus callosum and in four control subjects who were matched for age, gender, and handedness. In addition, the structural and emotional content of home dreams was compared for these two groups. Results indicate that acallosal subjects recalled fewer dreams in the laboratory than did control subjects, but recalled the same number of dreams at home. They also reported more contentless dreams in both situations. Furthermore, although acallosal subjects used fewer words to describe their dream content in both contexts, the number of content categories they reported differed little from the number reported by control subjects. However, some trends were found for acallosal's home dreams to differ from those of controls, i.e. more dreams with known characters and fewer dreams with unknown characters, animals, and colours. Differences in emotional contents were few; acallosals reported more distress than controls. The shorter length of acallosals' dreams might be explained, in part, by their lower verbal IQs. Other characteristics of dream content (e.g. more distress, fewer dreams with unknown and animal characters) may reflect limited social experiences in this group. However, the greater frequency of contentless dreams and the lower frequency of dreams with colour are trends consistent with the possibility that the corpus callosum may be implicated in processes of dream production and dream recall.

Journal Article↗

PubMed1993

Decreased interhemispheric EEG coherence during sleep in agenesis of the corpus callosum.

Inter- and intrahemispheric EEG coherence was studied in 4 subjects with agenesis of the corpus callosum (ACC) and in 4 matched controls through different states of the sleep/wakefulness cycle. Interhemispheric coherence was calculated between homologous prefrontal, frontal, central, parietal and occipital electrode pairs whereas intrahemispheric coherence was calculated between all adjacent, unihemispheric electrode pairs. EEG samples were recorded from stage 2, stages 3 + 4 and stage REM sleep and the eyes closed waking state. Interhemispheric coherence measures indicated lower values for ACC subjects than for control subjects for most brain regions; the occipital cortex was least affected. These results further validate the interhemispheric coherence function as a measure of activity in the corpus callosum and suggest that occipital measures may index activity localized in the posterior commissure. Intrahemispheric coherence measures indicated very few differences between the two groups, a result consistent with the suggestion that there is no specialized intrahemispheric compensation in ACC.

Adolescent↗

PubMed1993

Paradoxical improvement of residual vision following corpus callosotomy in brain damaged cats.

The nature of residual vision in cats having undergone serial lesions of various visual structures was investigated behaviorally. Following the section of the left optic tract, learning performance on brightness and pattern discrimination was normal; the additional lesion of all the known visual cortical areas of the right hemisphere greatly impaired retention and learning of pattern discriminations. When a corpus callosotomy was further performed, a paradoxical improvement in both the retention and learning of a pattern discrimination was observed. This hemispheric disconnexion, by interrupting the abnormal influences exerted by the lesioned side on the intact deafferented hemisphere, improved visual functions mediated by the latter.

Animals↗

PubMed1992

Influence of anatomical factors and spatial compatibility on the stimulus-response relationship in the absence of the corpus callosum.

Simple and choice reaction times (RTs) to lateralized flashes of light were measured in two acallosal subjects, a callosotomized patient with sparing of the splenium, six IQ-matched controls and six controls with above average IQ. The aim of the study was to investigate the influence of stimulus-response factors on visuomotor integration in the absence of the corpus callosum. The results showed that simple-RTs are faster for all groups when sensory input and motor output are coordinated in the same hemisphere, regardless of the spatial relationship between stimulus (S) and response (R). The difference between ipsilateral and contralateral RTs, taken as a measure of interhemispheric transmission time (ITT), was more than three times longer in the patients lacking the corpus callosum than in the controls. In the choice-RT paradigm, the main determinant of the response speed was S-R spatial compatibility rather than the anatomical relationship between the neural structures receiving the visual input and those controlling the motor output. Spatially compatible S-R pairings were always faster than incompatible pairings. The compatibility effect was present in all subjects but it was significantly larger in the callosum-deprived patients and their IQ-matched controls with respect to the high-IQ controls. The latter finding suggests that cognitive factors may be involved in the production of the spatial compatibility effect.

Adult↗

PubMed1992

Sleep architecture in agenesis of the corpus callosum: laboratory assessment of four cases.

Whether the corpus callosum is essential for normal human sleep cannot be decided from current knowledge. We thus studied sleep architecture in four subjects with agenesis of the corpus callosum (ACC) and four control subjects matched for age, gender, and hand preference. All-night EEG, EOG, and EMG activity were monitored in the laboratory for one adaptation night and one data acquisition night. Standard sleep variables were calculated for the second night. Agenesis subjects were found to have a greater percentage of stage 3 + 4 sleep and a lower percentage of stage 2 sleep than control subjects. Agenesis subjects also tended to have more REM sleep periods and a shorter REM cycle length than controls. The pattern of results is similar to that produced by partial callosotomy. It is also relevant to two hypotheses about the function of the corpus callosum in sleep. First, the corpus callosum may facilitate synchronization of activity between homologous regions in the two hemispheres but interfere with synchronization of neuronal populations within each hemisphere. Its absence may thus explain both an augmentation of slow-wave activity (and thus more slow-wave sleep) and a decrease in interhemispheric EEG coherence. Secondly, the corpus callosum may play a role in the regulation of the ultradian rhythm which underlies timing and duration of REM sleep.

Journal Article↗

PubMed1991

Absence of disconnexion syndrome in callosal agenesis and early callosotomy: brain reorganization or lack of structural specificity during ontogeny?

Four acallosal subjects, one child, aged 5, and three adults, as well as five epileptic patients who underwent callosotomy between the ages of 6-21 years, were tested on a variety of intra- and intermanual tasks in a study aimed at elucidating the developmental aspects of callosal plasticity. The performance of the clinical sample was compared to that of 48 normal children, aged 5-12 years, an age span generally considered to coincide with the final stages of callosal maturation. As previously reported, interhemispheric integration improved with increasing age in the normal sample. The two patients having undergone callosotomy in childhood performed as well as their normal peers, whereas the three others who had the operation in late adolescence or adulthood showed the typical disconnexion deficits reported in the literature. The acallosal subjects, including the youngest one, outperformed all groups. We speculate that the remarkable plasticity seen in the acallosals and the young callosotomized patients may be related to a critical period in development coinciding with a phase of synaptic overproduction and redundancy that would favor the reinforcement of alternative neural pathways. The compensatory mechanisms appear to become more limited in late adolescence when synaptic distribution presumably assumes adult patterns.

Adolescent↗

PubMed1991

Auditory lateralization for speech in language-impaired children.

The ability of five language-impaired (LI) children and five matched controls, aged 7-10 years, to discriminate natural pairs of consonant-vowel syllables contrasted on place of articulation and voicing, presented to the right or left ear with white noise in the contralateral ear, was investigated. The general pattern of errors indicated that LI children had more difficulty than controls in discriminating place of articulation contrasts only when they were presented to the left ear, as well as a difficulty in discriminating voice contrasts selective to the right ear. The results are discussed in terms of acoustic integration and suggest that bihemispheric dysfunction is a basis for specific language impairment.

Aphasia↗

PubMed1991

Target detection and movement discrimination in the blind field of hemispherectomized patients.

Four hemispherectomized patients were tested with a variety of tasks designed to investigate the extent of residual vision in the blind field. The first set of studies was aimed at evaluating the ability of these subjects to detect and localize at various eccentricities three types of targets which differed in their spatiotemporal properties (stationary, flashing and moving). The subjects could detect effectively the presence of any of these stimuli in their blind field and they experienced little difficulty in discerning blank from target trials. When manual pointing was used to measure localization quality, the hemianopes made more errors in their blind field but their accuracy, when detection was correct, was comparable with that observed in their intact visual field and in that of the control subjects. In the second set of experiments, the capacity of 3 of the subjects to detect in their blind field a moving grating, as well as to discriminate between relative grating velocities and directions in their blind field and in both fields simultaneously, was assessed. Two subjects could detect the movement in their blind field, although this was in part affected by stimulus velocity. When discrimination of relative velocities in the blind field and in both fields simultaneously was evaluated, individual differences were observed. However, all subjects showed some capacity to carry out the task. Finally, none of the experimental subjects was able to discriminate the relative directions of the moving gratings. The results are discussed in terms of collicular involvement to account for the residual vision observed in the blind field of hemispherectomized subjects.

Brain↗

PubMed1991

Psychological stress and psoriasis: experimental and prospective correlational studies.

Using a dismantled time-series design, 18 subjects with psoriasis symptoms on the scalp were randomly assigned to four groups and six dropped out: meditation (N = 5); meditation and imagery (N = 4); waiting list (N = 5); and no treatment control group (N = 4). Treatment lasted 12 weeks, with 4 weeks pre- and post-baseline periods. An assessment control group was also used during baseline periods (N = 4). The severity of psoriasis symptoms was reliably rated by dermatologists. A time-series multivariate regression analysis controlling for extraneous factors influencing psoriasis symptoms, revealed a significant difference between the mean psoriasis ratings of treatment and control groups after treatment (partial r = 0.30, p less than 0.01). No additional impact was associated with the use of the imagery technique (partial r = 0.06, p less than 0.05). Four subjects in the treatment groups, two in each condition, succeeded in clinically improving their psoriasis symptoms and none deteriorated. The practice of meditation may be clinically effective for some patients in reducing their psoriasis symptoms. For one of the control groups, the relation between psychological stress and psoriasis was examined prospectively over a period of 20 weeks using standardized measures. A time-series multivariate statistical method indicated an average positive correlation between the severity of psoriasis symptoms and psychological distress (partial r = 0.31, p less than 0.01) and the impact of adverse life events (partial r = 0.23, p less than 0.05); there were, however, important individual differences. Stress reduction techniques can thus be regarded as part of the treatment offered to some patients suffering from psoriasis.

Adult↗

PubMed1990

The corpus callosum and cerebral speech lateralization.

In order to specify the callosal involvement in the establishment of cerebral lateralization, a dichotic listening task was administered to six subjects with congenital absence of the corpus callosum, two callosotomized patients, and two hemispherectomized patients. The acallosal subjects were also compared to six subjects matched for age, sex, and hand dominance as well as to six subjects also matched for IQ. Our findings indicate that language functions, as assessed by dichotic listening performance, are more strongly lateralized in callosal agenesis subjects than in IQ-matched normal controls. Our results also reveal that hemispherectomized patients typically show a strong ear-advantage favoring the ear contralateral to their remaining hemisphere. Callosotomized patients, on the other hand, show a more variable pattern of results that seems to be related to the postsurgical time interval. Finally, our findings suggest that there might be a relationship between IQ and lateralization in subjects with borderline or mild deficiency.

Adolescent↗

PubMed1990

[Plasticity of the callosal system].

A series of experiments examined the potential plasticity of the callosal system in both epileptic patients and in kittens submitted to corpus callosotomy at various ages. The patients were tested for unilateral discrimination and interhemispheric transfer of tactile information. The youngest patient was also required to perform additional inter- and intrahemispheric comparisons of visual and tactile stimuli. The animals were tested for interhemispheric transfer of visual discriminations. The results suggest that in both animals and humans there exists a critical period before which callosal section does not disrupt interhemispheric communication. The results also indicate that the compensatory mechanisms used to achieve interhemispheric transfer in the absence of the corpus callosum may vary according to the sensory modality involved. The possible physiological and/or functional mechanisms responsible for callosal plasticity are discussed.

Adolescent↗

PubMed1988

Extent and limits of cerebral adjustment to early section or congenital absence of the corpus callosum.

The ability to effect inter- and intrahemispheric comparisons of visual and tactile stimuli was studied in 4 callosotomized patients and 6 callosal agenesis subjects using response accuracy and response times to determine the extent of cerebral adjustment to functional or congenital absence of the corpus callosum. The visual tasks involved within- and between-fields presentation of pairs of colours and shapes. The tactile tasks required uni- and bimanual comparisons of 3 categories of stimuli (size, shape and texture) of increasing difficulty. Older callosotomized children showed disconnection deficits similar to those reported in adult split-brain patients, whereas both acallosal subjects and our youngest patient with complete callosal transection demonstrated a high level of accuracy in the interhemispheric tasks. However, all patients required considerably more time to accomplish the cross-integration of relatively complex visual and tactile information which seems to be one of the major limitations of the compensatory mechanisms. The results also indicate that the quality of transfer differs between the acallosal and early-callosotomized patients in relation to the sensory modality studied. Thus, visual cross-matching was found to be superior to bimanual matching for the callosotomized group, whereas intermanual comparisons proved to be more efficient than visual integration in the acallosals. These divergent findings suggest not only that different compensatory mechanisms may be operating in visual and tactile transfer, but also that the same mechanisms may be utilized differently by the two populations deprived of the use of callosal connections.

Adolescent↗

PubMed1987

The relationship between callosal variation and lateralization in mice is genotype-dependent.

The relation between morphological variation of the corpus callosum and variation in the degree of paw preference was investigated in 129/J and BALB/cCF mice. A positive relationship explaining 24% of the variance of paw preference was found in 129/J mice; no such relationship exists in BALB/cCF mice. It is suggested that, since the genetic dissimilarity between these two inbred strains is comparable in magnitude with the genetic dissimilarity between unrelated human subjects, genetic variation may have been an uncontrolled source of heterogeneity in previous human neuropsychological studies.

Animals↗

PubMed1987

Psoriasis and stress: a prospective study.

In previous works, stress has been found to be related to psoriasis but only retrospectively and/or by means of nonstandardized measures. In our study the relationship between psoriasis and stress was examined prospectively over a period of 20 weeks by means of standardized measures. A multivariate statistical method indicated a positive correlation between the severity of psoriasis symptoms and psychologic distress (partial r = 0.31; p less than 0.01) and the impact of adverse life events (partial r = 0.23; p less than 0.05). According to these results, stress reduction could be regarded as part of the treatment offered to some patients suffering from psoriasis.

Adult↗

PubMed1986

Stereoperception in cats following section of the corpus callosum and/or the optic chiasma.

The spatial separation of the eyes in animals with overlapping visual fields means that parts of a three dimensional object project to slightly disparate retinal points in each eye. This disparity, once interpreted by the brain, is thought to be a sufficient condition for stereoperception. In the present experiment, stereopsis based on spatial disparity cues was evaluated in cats using Julesz random-dot stereograms before and after sections of the optic chiasm, the corpus callosum or both. Normal cats were able to solve the random-dot problem. Optic chiasm transection drastically diminished this ability, callosal section had little effect and combined lesions of these two structures abolished stereoperception. These results suggest that central stereopsis based on spatial disparity is mainly mediated by binocular cortical cells receiving their input via the ipsilateral and the through-the-chiasm contralateral thalamo-cortical pathways.

Animals↗

PubMed1986

Erythema induratum of Bazin.

Erythema induratum of Bazin is a rare entity, the cause and treatment of which are topics of continuing controversy. This report documents the cases of two patients with ulcerating leg nodules. One patient had concurrent active pulmonary tuberculosis, and the other had a history of previous treatment for pulmonary tuberculosis. The treatment regimen for these patients is outlined. First described by Bazin, the rare entity of erythema induratum was thought to be of tuberculous origin or a tuberculid reaction. Opinion has varied, and some authors have classified this condition as a vasculitis involving subcutaneous vessels. Because of the rarity of this disorder and the controversy surrounding its cause and pathogenesis, we share our experience with two patients whose clinical and pathologic findings were consistent with the diagnostic criteria for erythema induratum and in whom there was a recent or remote history of tuberculosis.

Adult↗

PubMed1986

Effects of early and late transection of the corpus callosum in children. A study of tactile and tactuomotor transfer and integration.

Five children, aged 6 to 16 years, were tested for unilateral discrimination and interhemispheric transfer of tactile information as well as tactuomotor learning at various intervals before and after therapeutic callosotomy. Comparison of preoperative and postoperative capacities revealed that younger children are considerably less affected by the interruption of callosal transmission than older children. Bilateral organization of speech and participation of the anterior commissure can largely be excluded as possible compensatory mechanisms. The most plausible explanation for the excellent preservation of interhemispheric integration of tactile functions in the younger patients appears to be continued reliance on ipsilateral pathways. The relatively greater deficits observed in the older children, on the other hand, suggest that sensorimotor functions come to depend more extensively on contralateral pathways as the corpus callosum reaches functional maturity.

Adolescent↗

PubMed1985

Acne fulminans with osteolytic lesions.

Multifocal lytic bone lesions were found in a patient with a severe form of acne. The clinical presentation was suggestive of "acne fulminans." Propionibacterium acnes was isolated from a subculture of bone tissue. The association of acne fulminans and osteolytic lesions is rare and the pathophysiology is unknown. However, the use of corticosteroids for systemic effect combined with local measures seems to give excellent treatment results.

Acne Vulgaris↗